Labeling adhesive

ABSTRACT

The use of dimer acids with conventional hot melt adhesive polymers provide adhesives particularly useful for bottle labeling. The label, along with the adhesive, can be easily removed from the bottle during the recycling process.

This is a divisional of application Ser. No. 10/428,890, filed May 5,2003.

FIELD OF THE INVENTION

The invention relates to the field of adhesives. More specifically theinvention relates to hot melt adhesives and the use thereof in removablelabeling applications.

BACKGROUND OF THE INVENTION

Both natural polymers and synthetic polymers have been used as basepolymers in bottle labeling adhesive applications. Natural polymer-basedadhesives, such as starch- and casein-based adhesives, can be formulatedto offer such advantages as good machinability, high wet strength, andice water resistance. Synthetic emulsion polymer-based adhesives provideadvantages such as, for example, a fast set time. Hot melt adhesivesbased on styrenic block copolymers are able to produce especially soft,often pressure sensitive adhesives, which are particularly effective inbonding plastic labeling films to plastic bottles. The increased use ofplastic labels and bottles has lead to the growth of hot melt adhesivetechnology. One disadvantage of hot melt adhesives is that they arehydrophobic and thus difficult to remove from the bottle after use intypical recycling operations.

A need continues to exist in the art for a hot melt adhesive that isuseful in bottle labeling applications and which is removable with thelabel from off a glass or plastic bottle. The current inventionaddresses this need.

SUMMARY OF THE INVENTION

The invention provides a labeled container, such as a bottle or jar,wherein the label is attached to the container using a hot melt adhesivecomprising an acid-functional diluent, preferably a dimer acid. Thelabel can be easily removed from the container during the recyclingprocess by application of alkaline water. The invention provides the artwith a method of recycling a labeled bottle, jar or like containerwhereby the label is easily removed from the container without leavingany adhesive residue on the bottle.

One aspect of the invention is directed to a hot melt adhesiveformulation that is particularly advantageous for use in bottle labelingapplications. The adhesive of the invention comprises an acid functionaldiluent, a styrenic block copolymer and a tackifier. In one embodimentthe adhesive also comprises a plasticizer.

Another aspect of the invention is directed to a method for bonding afirst substrate to a second substrate comprising applying to a surfaceof at least one of said first and/or second substrate the adhesivecomposition of the invention. Preferably, the first substrate is a labeland said second substrate is a container. Particularly preferred for usein the method of the invention are plastic and glass containers, such asjars, bottles and the like.

Still another aspect of the invention is directed to an articlecomprising a label, wherein the label is attached to the article by theadhesive described herein. In one embodiment of the article of theinvention is a glass or plastic article comprising a paper or plasticlabel.

Yet another aspect of the invention is a method of removing a label froma container, the method comprising contacting a labeled container withalkaline water.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides an adhesive, a method for bonding a firstsubstrate to a second substrate, articles manufactured using theadhesive of the invention, in particular labeled bottles and jars and amethod of removing a label from a bottle or jar.

The invention provides the labeling industry with new kinds ofrecyclable labeling adhesives useful for applying labels onto glass orplastic containers. The adhesive has strong tack to hold the label onthe glass or plastic substrate and satisfactorily secures the plasticlabel to the glass within a short time. Moreover, the adhesive of theinvention may be applied using conventional high-speed labelers such aspallet transfer rotary labelers of the type manufactured by Krones, Ltd.or Trine Labeling Systems.

Acid functional diluents have a carboxylic acid group and exhibit anacid number greater than 100, preferably greater than 150, and mostpreferably about 200. Included in this group are fatty acids and theirhydrogenated derivatives such as oleic acid, linoleic acid, andisostearic acid. Acid functionalization can be obtained on variousdiluents by free radical grafting of maleic anhydride. Alternativelyvinyl monomers can be copolymerized with acid functional monomers.Examples are the copolymerization of ethylene or styrene with maleicanhydride or ethylene with acrylic acid. These acid functional diluentscan be liquids or waxy solids, but most preferably are liquids for speedof reaction in aqueous base. Most preferred are liquid diluents withmore than one acid site per molecule and with a molecular weight above250 g/mol. Higher molecular weights minimize volatility in the hot melttank. Most preferred are “dimer acids” with a molecular weight of about500 and an acid number of from about 190 to about 200.

“Dimer acids” are polymeric fatty acids which are derived fromunsaturated fatty acids, typically C₁₈ acids such as oleic, linoleic andlinolenic acid. Because of their ready availability and relative ease ofpolymerization, oleic and linoleic acids are the preferred startingmaterials for the preparation of the polymeric fatty acid resins usedherein. Mixtures of these two acids are found in tall oil fatty acidsand, accordingly, commercial tall oil fatty acids are a common sourcefor preparing the described polymeric fatty acid resins. Representativeof polymeric fatty acids are those commercially available from thepolymerization of tall oil fatty acids. The polymeric fatty acids usedherein, sometimes referred to in the art as “dimer acids”, are complexmixtures resulting from the polymerization of fatty acids. Thecomposition of these polymeric fatty acids are typically 0-5% by weightC₁₈ monobasic acids (monomer), 60-95% by weight C₃₆ dibasic acids(dimer) and 1-35% by weight C₅₄ and higher polybasic acids (trimer).

These polymeric multiacids are prepared by self condensation ofunsaturated fatty acids to produce “dimer” acids. However, thedimerization process typically produces up to about 25% of triacid aswell. The relative ratios of monomer, dimer, and trimer inunfractionated polymeric fatty acids are dependent on the nature of thestarting material and the conditions of polymerization. For purposes ofthis invention the term dimer acid is meant to include small amounts oftrimer acid. The preparation of these dimer acids is further describedin Encyclopedia of Chemical Technology, “Dimer Acids”, E. Leonard, 3ed., vol. 7, p. 768, Wiley (1979). Methods for the polymerization offatty acids are described, for example, in U.S. Pat. No. 3,157,681. Thepolymeric fatty acids may be unhydrogenated or hydrogenated. Aparticularly suitable acid functional diluent is Pripol 1013 dimer acid,which has an acid number of 196 and is available from Uniqema.

Various tackifiers are suitable for use in the invention. These includehydrocarbon resins, synthetic polyterpenes, rosin esters, naturalterpenes, rosin, and the like as are well known to those skilled in theart (see C. W. Paul, “Hot Melt Adhesives”, in Adhesion Science andEngineering, volume 2, Surfaces, Chemistry & Applications, M. Chaudhuryand A. V. Pocius editors, Elsevier, New York, 2002, p. 711). Preferredare acid functional tackifiers such as rosin, hydrogenated rosin, andmaleated rosin, with and acid number above 100. Most preferred ishydrogenated rosin. One such material is Foral AX, which is hydrogenatedwood rosin and has an acid number of 130; it is available from Hercules.The tackifying agent will generally be present at a level of from about35 to about 75% by weight of the adhesive composition and preferably ata level of at least about 45% by weight.

In one embodiment, the adhesive comprises from about 10% to about 35 wt% of a dimer acid, from about 10 to about 30 wt % of a styrenic blockcopolymer, and from about 35 to about 75 wt % of a rosin tackifier.

The invention also provides a process for bonding a substrate to asimilar or dissimilar substrate using the adhesive. The processcomprises applying to at least a portion of at least a first substrate amolten hot melt, bringing a second substrate in contact with theadhesive present on the first substrate, and allowing the adhesive tosolidify, whereby the first substrate is bonded to the second substrate.

The invention further provides articles of manufacture comprising theadhesive. The properties of the adhesive makes it particularly useful asa labeling adhesive.

The adhesives of the invention may be formulated for application at lowtemperatures, i.e., formulations that can be applied at temperaturesbelow about 160° C., preferable below about 140° C., and most preferablybelow about 120° C.

The polymers used to prepare the adhesive of the invention are based onrubbery block copolymers. These polymers include the block ormulti-block copolymers having the general configuration: A-B-A orA-B-A-B-A-B- wherein the polymer blocks A are non-elastomeric polymerblocks which, as homopolymers have glass transition temperatures above20° C., while the elastomeric polymer blocks B are butadiene or isopreneor butadiene and isoprene which is partially or substantiallyhydrogenated. Both linear and/or branched may be used in the practice ofthe invention. Typical branched structures contain an elastomericportion with at least three branches that can radiate out from a centralhub or can be otherwise coupled together.

The non-elastomeric blocks may comprise homopolymers or copolymers ofvinyl monomers such as vinyl arenes, vinyl pyridines, vinyl halides andvinyl carboxylates, as well as acrylic monomers such as acrylonitrile,methacrylonitrile, esters of acrylic acids, etc. Monovinyl aromatichydrocarbons include particularly those of the benzene series such asstyrene, vinyl toluene, vinyl xylene, ethyl vinyl benzene as well asdicyclic monovinyl compounds such as vinyl naphthalene and the like.Other non-elastomeric polymer blocks may be derived from alpha olefins,alkylene oxides, acetals, urethanes, etc.

The elastomeric block component of the copolymer may be isoprene orbutadiene that may or may not be hydrogenated. This hydrogenation may beeither partial or substantially complete. Selected conditions may beemployed for example to hydrogenate the elastomeric block while not somodifying the vinyl arene polymer blocks. Other conditions may be chosento hydrogenate substantially uniformly along the polymer chain, both theelastomeric and non-elastomeric blocks thereof being hydrogenated topractically the same extent, which may be either partial orsubstantially complete.

Typical of the rubbery block copolymers useful herein are thepolystyrene-polybutadiene-polystyrene (SBS),polystyrene-polyisoprene-polystyrene (SIS) and e.g.,polystyrene-poly-(ethylenebutylene)-polystyrene (SEBS) andpolystyrene-poly-(ethylenepropylene)-polystyrene (SEPS). Thesecopolymers may be prepared using methods taught, for example, in U.S.Pat. Nos. 3,239,478; 3,427,269; 3,700,633; 3,753,936; and 3,932,327.Alternatively, they may be obtained from Kraton Polymers under thetrademarks Kraton 1101, 1102, 1107, 1650, 1652 and 1657; from Enichemunder the Europrene Sol-T tradenames; from Firestone under the tradenameStereon 840A, and from Dexco Polymers under the tradename Vector.Mixtures of copolymers, such as blends of SBS and SIS, may also be used.To minimize viscosity and maximize processibility on labeling machinesthe melt index of the base polymers (grams/10 minutes at 200° C./5kg—ASTM D1238 (Condition G)) is preferably above 5 and most preferablyabove 20.

The block copolymer component will generally be present at a level offrom about 10 to about 30% by weight of the adhesive composition, moretypically at levels of about 14% to about 22%.

The present invention optionally also includes 0 to about 20 weightpercent of an endblock resin which is substantially aromatic. Examplesof such endblock resins can be prepared from any substantially aromaticmonomers having a polymerizable unsaturated group. Typical examples ofsuch aromatic monomers include the styrenic monomers, styrene,alphamethyl styrene, vinyl toluene, methoxy styrene, tertiary butylstyrene, chlorostyrene, etc., coumarone, indene monomers includingindene, and methyl indene. The aromatic endblock resin is preferablypresent in amounts of 5 to 20 weight percent. Preferred is HERCOLITE 240or KRISTALEX 5140, both of which are alpha methyl styrene resinsavailable from Hercules, Inc.

The present invention also optionally includes 0 to about 20 weightpercent of a plasticizer. These plasticizers include materials which areliquid diluents, but do not have a high acid functionality (i.e. acidnumber is <100). Such liquid diluents include plasticizing or extendingoils or liquid tackifiers, including olefin oligomers and low molecularweight polymers as well as vegetable and animal oil and theirderivatives. The petroleum derived oils which may be employed arerelatively high boiling materials containing only a minor proportion ofaromatic hydrocarbons (preferably less than 30%, more particularly, lessthan 15% by weight of the oil). Alternatively, the oil may be totallynon-aromatic. Suitable oligomers include polypropylenes, polybutenes,hydrogenated polyisoprene, hydrogenated polybutadiene, or the likehaving average molecular weights between about 350 and about 10,000.Preferred are LUMINOL T350, a mineral oil available from Petrocanada andKAYDOL OIL available from Witco Corporation.

Other plasticizers include phthalates such as dioctyl phthalate,polyesters such as Paraplex G-59 available from C.P. Hall Company,adipates such as dioctyl adipate, epoxidized soybean oil, trimellitates,such as triisooctyl trimellitate, sulfonamides such as N-octylparatoluene sulfonamide, citrates such as triethyl citrate, phosphateesters such as 2-ethyl hexyl diphenyl phosphate, and benzoates such asdiethylene glycol dibenzoate, and the like. Preferred plasticizers arethose with some level of water sensitivity by virtue of their polarity.For example, materials containing ether, hydroxy, ester, phosphate,ester, sulfonamide, and phosphate groups. Most preferred arepolyalkylene glycol benzoates such as Benzoflex 2088 which is adibenzoate derived from a mixture of polyalkylene glycols (diethyleneglycol, trietheylene glycol, and dipropylene glycol) and is availablefrom Velsicol Chemical Corp.

An antioxidant or stabilizer may also be included in the adhesivecompositions described herein in amounts of up to about 3% by weight,more typically in amounts of about 0.5%. Among the stabilizers orantioxidants useful herein are the hindered phenols or hindered phenolsin combination with a secondary antioxidant such as distearylthiodipropionate (“DSTDP”) or dilauryl thio-dipropionate (“DLTDP”).Representative hindered phenols include: 1,3,5-trimethyl 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; pentaerythrityltetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; pentaerythritoltetrakis (3-lauryl thiodipropionate);n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenol)-propionate;4,4′-methylenebis (2,6-tert-butylphenol); 4,4′-thiobis(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol;6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-triazine;di-n-octadecyl 3,5-di-tert-butyl-4-hydroxy-benzyl-phosphonate;2-(n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitolhexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate]. Preferred areIRGAFOS 168, a secondary antioxidant available from Ciba and IRGANOX1010, a hindered phenol primary antioxidant available from Ciba-Geigy.Other antioxidants include ETHANOX 330, a hindered phenol fromAlbermarle; SANTOVAR, a 2,5 ditert-amyl hydroquinone from Monsanto; andNAVAGARD P a tris (p-nonylphenyl)phosphite from Uniroyal.

Other additives conventionally used in hot melt adhesives to satisfydifferent properties and meet specific application requirements also maybe added to the adhesive composition of this invention. Such additivesinclude, for example, fillers, pigments, flow modifiers, dyestuffs,which may be incorporated in minor or larger amounts into the adhesiveformulation, depending on the purpose.

Hot melt adhesives may be prepared using techniques known in the art.Typically, the adhesive compositions are prepared by blending thecomponents in the melt at a temperature of about 100° to 200° C. until ahomogeneous blend is obtained, generally about two hours. Variousmethods of blending are known and any method that produces a homogeneousblend is satisfactory.

The properties of the invention make it particularly useful in, e.g., inbottle labeling or other applications involving plastic bonding.

The adhesive is applied to a substrate while in its molten state andcooled to harden the adhesive layer. The adhesive product can be appliedto a substrate such a plastic or glass article by a variety of methodsincluding coating or spraying in an amount sufficient to cause thearticle to adhere to another substrate or an unrelated material such asa low density polyolefin or other conventionally employed substrates.

While the adhesive finds particular use as a labeling adhesive, otheruses are clearly contemplated and are encompassed by the invention. Theadhesive described herein may be used for, e.g., laminating.

As used herein, a “container” means a jar, bottle, can or canister,bucket, beaker and the like. The container may be made of glass, plasticor metal. Specific examples include, but are not limited to soft drinkbottles, beer bottles, wine bottles, salad dressing bottles, sauce jars,condiment jars, and the like. The container may be made of any type ofmaterial including but not limited to wood, glass, metal, plastic orpoly and plastic-coated glass.

As used herein and a “label” means e.g. a material having a surface towhich an adhesive is applied. The label may be made of any type ofmaterial, including but not limited to paper, plastic or metallizedpaper and the like. Labels may be of any size or shape. While the labelmay be opaque, use of plastic labels wherein at least a portion istransparent is comtemplated. By “transparent” means that at least aportion of the label is substantially clear, i.e., the surface of thesubstrate to which the label has been applied is visible through thelabel and adhesive.

Use of the adhesives of the invention to bond labels to glass or plasticsubstrates is particularly advantageous.

Plastic as used herein refers to the material used to make e.g., foodand other storage containers and/or labels include polyethylene,polypropylene, polystyrene, polycarbonate, polyvinylchloride, highdensity polyethylene (HDPE) and polyethylene terephthalate (PET).

To attach the labels to the article, the adhesive is applied to thesurface of the container or, when using a high speed labeler, directlyto the label. The label and the article are then contacted underpressure and the adhesive bond allowed to set. The amount of pressureand the time need to set the bond will depend upon the type ofcontainer, label, and the particular adhesive formulation used.

Recycling of label bottles involves washing the article usually in analkaline water solution (i.e. water with a base added to raise the pHabove 7, typically at least about 12 or more). The water may or may notbe heated and the agitation levels vary. For good removal in the varietyof processes that currently exist it is important that the adhesive behighly sensitive to base. The high level of acid functionality in theadhesive provides this sensitivity.

The following examples are for purpose of illustration and not intendedto limit the scope of the invention in any manner.

EXAMPLES Example 1

An adhesive formulation (Sample 1) was prepared that comprised 12 weight% Vector 4411 (an SIS block copolymer available from Dexco with a meltindex of 40), 6 weight % Quintac SL-117 (an SIS block copolymeravailable from Nippon Zeon with a melt index of 65), 5 weight %Hercolite 240 (aromatic hydrocarbon tackifier available from HerculesInc. (end block resin)), 21 weight % Pripol 1013 (dimer acid availablefrom Uniqema), 56 weight % Foral AX (a hydrogenated rosin tackifieravailable from Hercules Inc.) and 0.5 weight % Irganox 1010 (anantioxidant available from Ciba-Geigy Inc.)

Adhesive Sample 1 was characterized and compared to three commerciallyavailable styrenic block copolymer based pressure sensitive hot meltadhesives (Comparative Samples A, B and C). Sample A (Etm 1051), B (Etm89e) and Sample C (Etm 128) are commercially available from NationalStarch and Chemical Company, Bridgewater, N.J. Viscosity was measured inBrookfield viscometer using a number 27 spindle. Each adhesive was usedto attach polypropylene labels to PET bottles. The labeled sections werecut out of the bottles and sent to an independent industry test lab(United Resource Recovery Corporation (URRC), Spartanburg, S.C.) fordetermining their potential to perform in standard recycling processes.Their test involves exposing the samples to an aqueous caustic wash withsome heat. The details are proprietary to the company. All of thecommercial glues (ETM 1051, 89e, and 128) left adhesive residue on thePET flakes after the process. None of the adhesive from Sample 1remained on the flakes after the process. Results are shown in Table 1.TABLE 1 Properties Sample A Sample B Sample C Sample 1 Viscosity @130°C. 2300 cP 900 cP 1000 cP 1500 cP Initial Colour Water Water Yellow Palewhite white Yellow URRC Recyclability fail fail fail pass Test

Example 2

An adhesive formulation (Sample 2) was prepared that comprised 6 weight% Vector 4114 (an SIS block copolymer available from Dexco, with a meltindex of 24), 12 weight % Vector 4411 (an SIS block copolymer availablefrom Dexco), 20 weight % Pripol 1013 (dimer acid available fromUniqema), 51.6 weight % YT 102 AX (a gum rosin tackifier available fromYser Resins), 10 weight % of Benzoflex 2088 (plasticizer), 0.2 weight %Irganox 1010 and 0.2 weight % Irganox 168 (antioxidants available fromCiba-Geigy Inc.).

Adhesive films (60 mm×10 mm and 200 microns thick) were bonded to dry 80mm×20 mm sections of a PET bottle provided by PETCYCLE, and thenweighed. The adhesive-coated PET pieces were then washed in watercontaining 2.5% NaOH (caustic) at 80° C. for 8 minutes. The PET pieceswere then removed, washed in neutral water, dried, and weighed. Theweight % of adhesive removed from the strips is then determinedgravimetrically. This lab test is designed to mimic the PETCYCLE test.PETCYCLE is a bottle recycling company in Bad Neuenahr-Ahrweiler,Germany. Adhesive removal by this lab test is shown in Table 2. TABLE 2Adhesive % Removed Sample 1 97 Sample 2 93 Sample A 61 Sample B 55Sample C 49

Sample 2 was also submitted to PETCYCLE and was judged to removeadequately from PET bottles in their actual process.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A process for bonding a label to a container comprising applying toat least one substrate surface of a label and/or a container anadhesive, said adhesive comprising a styrenic block copolymer, atackifier, and an acid functional diluent with an acid number of atleast 100, and bringing the substrate surface of said label in contactwith the substrate surface of said container.
 2. The process of claim 1wherein the adhesive further comprises a plasticizer and/or an end blockresin.
 3. The process of claim 1 wherein the adhesive comprises fromabout 10 to about 30% by weight of styrenic block copolymer, from about35 to about 75% by weight of a tackifier, from about 10 to about 35% byweight of an acid functional diluent with an acid number of at least100, and up to about 20% of a plasticizer and/or end block resin.
 4. Theprocess of claim 1 wherein the styrenic block copolymer has a melt indexof >20.
 5. The process of claim 4 wherein the styrenic block copolymeris present at a level of 14-22% by weight.
 6. The process of claim 1where the acid functional diluent is a dimer acid.
 7. The process ofclaim 1 where the tackifier is an acid functional tackifier with an acidnumber of at least
 100. 8. The process of claim 1 comprising up to about20% of a benzoate plasticizer.
 9. The process of claim 1 where thestyrenic block copolymer has a melt index of >20, the acid functionaldiluent is dimer acid, and the tackifier is rosin.
 10. The process ofclaim 1 wherein said label is made of paper or plastic and saidcontainer is a bottle or jar made of glass, metal, or plastic.
 11. Amethod of removing a label from a labeled container, wherein said labelwas applied to the container using the process of claim 1, the removalmethod comprising contacting a labeled container with an alkalinesolution.
 12. The method of claim 11 wherein the acid functional diluentis a dimer acid.
 13. The method of claim 11 wherein the styrenic blockcopolymer has a melt index of >20 and the tackifier is acid functionalwith an acid number of at least
 100. 14. The method of claim 13 whereinthe acid functional diluent is a dimer acid.
 15. The method of claim 11where the styrenic block copolymer has a melt index of >20, the acidfunctional diluent is dimer acid, and the tackifier is rosin.
 16. Anarticle comprising a label, wherein the label is attached to the articleusing the process of claim
 1. 17. The article of claim 16 wherein theacid functional diluent is a dimer acid.
 18. The article of claim 16wherein the styrenic block copolymer has a melt index of >20 and thetackifier is acid functional with an acid number of at least
 100. 19.The article of claim 18 wherein the acid functional diluent is a dimeracid.
 20. The article of claim 16 where the styrenic block copolymer hasa melt index of >20, the acid functional diluent is dimer acid, and thetackifier is rosin.